This application is based on Japanese Patent Applications No. 2001-161088 filed on May 29, 2001, and No. 2001-204025 filed on Jul. 4, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a knock control apparatus for an engine.
2. Description of Related Art
JP-B2-2621396 discloses a knock control apparatus that varies ignition timing in response to a detected octane rating of fuel. The apparatus prevents a knock in a stable condition of the engine such as a constant speed condition. But, in a transitional condition, delays for detecting an intake air amount and an engine rotational speed (engine speed) affect the ignition control, and condition of a combustion chamber varies in accordance with the transitional condition. Therefore, it is difficult to reduce knock when the engine is in a transitional condition such as an accelerating condition.
JP-A-4-203266 discloses an ignition timing control apparatus for varying ignition timing to provide a fine drivability when the engine is in the transitional condition. However, the apparatus does not utilize a knock control apparatus, therefore it is difficult to reduce knock in transitional conditions.
U.S. Pat. No. 4,617,895 (JP-B2-6-60621) discloses a knock control apparatus that uses a statistical process for detecting an occurrence of knock. The above apparatus uses a threshold level to determine the occurrence of knock. In this apparatus, it is difficult to determine the threshold level to discriminate signal and noise.
U.S. patent application Publication US2001/0015198A1 discloses a knock control apparatus that detects a knock based on waveform characteristics of sensor signal. Therefore, it is difficult to detect a knock accurately, especially in a range in which the sensor signal level is low.
It is an object of the present invention to provide a knock control apparatus for engine that is capable of controlling a knock accurately.
It is another object of the present invention to provide a knock control apparatus for engine that is capable of controlling a knock accurately in a transitional condition.
It is a still another object of the present invention to achieve the above object even if a knock occurrence condition is changed by an influence of a knock related parameters such as an octane rating, a deposit and aging of the engine.
It is a yet another object of the present invention to provide a knock control apparatus for engine that is capable of detecting a knock accurately.
According to a first aspect of the present invention, a knock control apparatus for engine comprises base ignition timing setting means for setting a base ignition timing in accordance with an operating condition of the engine, knock determining means for determining an occurrence of knock, retard value setting means for setting a retard value for retarding the base ignition timing when the occurrence of knock is determined. Therefore, the apparatus reduces knock by retarding the ignition timing based on the retard value. The apparatus further comprises retard value learning means for learning a learned value based on the retard value, base retard value setting means for setting a base retard value in accordance with an accelerating condition when an acceleration of the engine is determined, final corrective value setting means for setting a corrective value by correcting the base retard value based on the learned value, and ignition timing setting means for setting an ignition timing when the engine is in an acceleration, the ignition timing being set based on the base ignition timing and the corrective value. In this arrangement, the ignition timing in an acceleration condition is corrected based on the corrective value that reflects the learned value. Therefore, it is possible to reflect the retard value for reducing knock on the ignition timing in the acceleration condition.
According to a second aspect of the present invention, a knock control apparatus for engine, comprises a knock sensor that detects a knock of the engine, and a plurality of knock determining means for determining an occurrence of knock respectively, the determining means utilizing different processes for determining the occurrence of knock based on a sensor signal of the knock sensor, final determining means for determining an occurrence of knock based on the determinations of the plurality of determining means, and ignition timing controlling means for controlling an ignition timing based on the determination of the final determining means. Therefore, it is possible to improve the accuracy of determination of knock.
The plurality of knock determining means may include at least two of knock determining means such as statistical knock determining means for determining an occurrence of knock by utilizing a statistical process that processes the sensor signal, waveform knock determining means for determining an occurrence of knock based on a waveform characteristic of the sensor signal, and frequency analyzing knock determining means for determining an occurrence of knock by utilizing a frequency analyzing process that processes the sensor signal.